The controlled application and removal of power to loads, such as electronic circuitry, can be performed in a multiplicity of different ways. Mechanical switches require that the user physically move electrical contacts in the switch to connect the power source to the load. Electromechanical relays respond to an electronic control signal supplied by the user to close a set of contacts so as to connect power to the load. While such mechanical and electromechanical configurations exhibit certain ideal switch characteristics, such as near infinite "off" impedance, near zero "on" impedance, and zero quiescent current, they suffer from certain disadvantages such as susceptibility to mechanical failure, the requirement of control signals of moderate power, slow response time, switch bounce, and degradation in performance after a certain number of on/off cycles.
A number of solid state switches are presently available in both bipolar and MOS or DMOS technologies. While the MOS type switches feature low quiescent currents, they suffer from a lack of speed, for example switching times of 30 to 50 microseconds. While these speeds are an improvement over the mechanical and electromechanical switch technologies, they are still too slow for some applications.
Present bipolar switches are fast, having for example 1 microsecond switching times, but require significant standby or quiescent currents. The existing bipolar switch technology can be modified by conventional approaches to operate at lower quiescent currents. However, with such conventional approaches, speed is sacrificed; i.e. the switching speeds of such modified bipolar devices will be on the order of MOS device switching speeds.
Advantages of solid state switches include the absence of mechanical type failures, the requirement of lower level control signals, and potentially smaller physical size.
It would therefore be highly desirable to have a solid state bipolar switch having fast switching times and low or no standby current requirements, in addition to infinite impedance in its "off" state and zero impedance in its "on" state.